In recent years, there have been developed an electric vehicle, a hybrid vehicle, and a fuel-cell vehicle, whose motor is driven by a power supply of much higher voltage to propel the vehicle when compared to a battery of approximately 12 volt mounted on a conventional motor vehicle. For each of these vehicles having a high-voltage electric system, it is necessary to quickly interrupt the high-voltage power supply system thereof to prevent vehicle fire and electric shock accident in the case of impact. When the high-voltage system is interrupted, however, it is impossible to move the vehicle, and thus malfunction should be avoided.
For example, Japanese Patent Laying-Open No. 2002-354602 discloses a technique of using an impact sensor provided for inflating an air bag to interrupt a high-voltage system when the impact sensor senses an impact.
However, there may be a case where the interruption of the high-voltage system based on an output of the air bag impact sensor for activating an air bag is insufficient. In other words, the air bag impact sensor is configured to inflate an air bag only when a seat belt alone can cause injury to a passenger because the cost incurred to repair an air bag, for example, is large when it is once activated.
Instead, a high-voltage power supply system is required to be interrupted when a high-voltage electric system contained in an engine room on the front or rear side of the vehicle may be damaged due to an impact. Accordingly, it is preferable to determine whether a high-voltage power supply system is interrupted based on a criterion different from that for inflating an air bag.
Alternatively, it may be possible to provide an impact sensor designed specifically for determining whether a high-voltage power supply system is interrupted. In this case, it is necessary to prevent a malfunction of the impact sensor in the case of tampering such as a strike with a hammer in the periphery thereof. As a preventive measure against a malfunction, it may be possible to adopt following criteria (1) and (2) to exclude the case where such tampering may occur.
(1) When a shift position is in a parking range or in a neutral range, a high-voltage is not transferred to generate driving force. Therefore, a determination as to whether the vehicle is damaged is not made.
(2) When the vehicle is at low speed, a determination as to whether the vehicle is damaged is not made.
However, when criteria such as (1) and (2) above are adopted, there may be a case where, although it is preferable to interrupt a high-voltage power supply system, the high-voltage power supply cannot be interrupted in the event of a passive accident, namely, an accident caused by being collided by another vehicle during a temporal stop, for example, or an accident caused by changing a shift position to a neutral range while driving.
As a preventive measure against tampering such as a strike against the vehicle with a hammer, it may be possible to adopt a redundant system for an impact sensing portion. However, an additional impact sensor is needed, which causes an increase in cost and requires a mounting space therefor. Accordingly, it is difficult to implement such a measure.